The game of golf involves striking a golf ball with sufficient force and accuracy to reach the putting green. Typically, up to 13 different clubs are used to do this. On the putting green, only one club is used for hitting the ball in the hole, i.e., the putter. For a golf course rating, par is determined by the number of strokes a “good” golfer would take to complete the hole. If shooting par, half the strokes are putts. Hence the putter is the most important golf club.
The putting stroke is completely different than the golf swing needed to reach the green. Putting requires gentle striking of the golf ball to get it in the hole. Precise control of the direction and distance for putting the ball, as well as the ability to read the green to know where to hit the ball to account for any curvature on the green surface, are the physical aspects of putting. Mental attitude and being comfortable with making the putt are equally important. Putting is frequently thought to be more of an art than science, but numerous technological developments have been made in the recent times to improve all golf equipment, including some putter aspects.
Putters consist of a head, shaft, and grip. The original putter heads were flat or blade-like. Many modern putter heads are much bigger to increase the moment-of-inertial (MOI), so that when impacting the ball, the face the putter head doesn't twist with an off center hit. The MOI development increases the confidence to the golfer as well. Many other developments for putters have been made such as; making a better contact surface on the putter face to get the ball rolling sooner, making the grip larger to give a better feel, etc.
Modern putters with higher MOI heads have greater balancing concerns at the golfer's grip position. When holding the putter in the normal lie-position (the head under the golfer's eyes), these balancing issues cause the large bending moment to the putter perpendicular to the putting direction, torsion of the putter head to twist in the golfer's grip, and a slight moment wanting to twist the putter face to a higher loft. These undesirable moments and torsion require the golfer to subconsciously correct for these loading directions during the putting stroke, masking the feeling of what is essential to make a good putting stroke. Such unbalanced moments/torques and corrections for them can cause the putter head to wobble along the swing path as well as increasing the required grip pressure by the golfer. The better feel from elimination of these undesired moments and torques also improves the mental confidence at the same time.
One of the aspects of putter design that is starting to get attention is the advantage of balancing. Several patents exist for putting small axisymmetric weights (relative to this patent application) in the end of the shaft. That weight moves the center of gravity of the putter very slightly closer to the grip, but the center of gravity along the shaft is still closer to the putter head than where the golfer grips the club. Other patents describe how to eliminate the torsion from the putter head weight, but still leave the main “lifting moment” at the golfer's grip. This patent teaches how to completely eliminate the bending moments in different directions and torsion at the golfer's grip position by adjustable balancing done in the grip so it can be applied to any putter.
The present invention recognizes that there are three relevant degrees-of-freedom of putter motion and corresponding moments and torques for complete balancing at the centroid of the golfer's grip when the putter is held in the normal lie-position (under the golfer's eyes). The present invention provides an offset or nonsymmetrical, adjustable balancing weight system that is concentrated at the upper part of the grip that follows all United States Golf Association (USGA) grip requirements (described later). Counter balancing of a modern high-moment-of-inertia (MOI) putter requires a significant mass above the golfer's grip position that cannot be accomplished with a weight inside the shaft (even if depleted uranium or gold was used). Modern high MOI putter heads have a much larger mass than the original blade putters of early golf. The higher mass provided by the present invention controls three detrimental aspects to the golfer's ability to “feel” the putt by creating; (a) a bending, or lifting, moment in the plane perpendicular to the putting direction to counteract the putter head weight, (b) a bending, or loft-increasing, moment that wants to counteract the increase of loft of the putter face that comes from the center of mass of the putter head being behind the shaft, and (c) a torque at the grip position to counteract the torsion induced from the putter head wanting to twist under the shaft.
The “feel” of the putter is affected by the following aspects: (i) The actual gravity or dead-weight of the putter—that's unchangeable; (ii) The force required swinging the putter as desired—that is the force you want to be the largest percentage of the forces/moments that the golfer's hand “feel”; (iii) The moment/force required by the golfer to lift the putter to the lie position under his eyes (also called the “lifting moment”). The putter might be at approximately a 70-degree angle, but that is variable with putter design and the golfer's preferences. This is the largest nonessential moment/torque/force the golfer feels and is the primary balance axis of the proposed balancing system. Many patents talk about balancing in this direction, but not to the magnitude needed for high MOI putters and having it adjustable to the centroid of the golfer's grip position; (iv) In the lie-position under the golfer's eyes (˜70-degree shaft angle from the ground), virtually all modern putters will twist into an open position (also called the “head torque”). The hands of the golfer need to twist the putter face back to the square position. This torque adds additional forces on the golfer's hands that further mask the “feel” of the putt forces that are need to strike the ball. There is an internal offset mass in the proposed balancing weight that is adjustable to counteract the torsion that is imposed on the golfer's hands when the putter is in the lie-position. In the preferred application there are a series of holes where different size weights can be inserted to provide the face-balancing compensation for the lie-position depending on the putter design and where the golfer grips the club; (v) The offset centroid of the putter head also creates a smaller moment that wants to increase the loft of the putter face (called the “loft-increasing moment”). This increased loft is undesirable since it makes the ball bounce rather than roll after initial impact.
Although the location of the main balance-weight body provided by the present invention is adjustable, the main balance-weight body within the grip must be locked into place to maintain the balance position. The balancing in the three degrees-of-freedom of motion can be accomplished in either a split-grip option or single grip option, although some details differ with the two options, the basic principle is identical. During the initial fit-up with the split-grip option, set screws are used to adjust the upper balance-weight body up and down the shaft to do the primary putter “lifting-moment” balancing described in (iii) above. The length of the main balance-weight body consists of two pieces in a split-grip option, typically using a shorter aluminum or stainless steel piece for the bottom with an upper stainless steel section. (The material used for this lower section may vary with the weight of the putter head, and similarly a higher density material could be used for the upper part). The lower balance-weight body is locked in at the lifting-moment balance location. The heavier stainless steel part on the top can then be rotated so the symmetric position of a set of internal offset holes is lined up with the centroid of the mass of the putter head.
If there is too much torque-balancing correction without filling the internal offset holes, then rods of different lengths and density are inserted into the internal offset holes to change the offsetting mass. These rods must be locked in place with an adhesive when the balancing is completed. If more torsional offset is needed, then offset holes in the lower balance-weight body are filled with different masses for additional torsion balancing. If the moment (causing the face to have more loft) exists after the torque-balancing operation, then the inserted weights and rotation of the upper balance-weight body can be adjusted so that the loft-increasing moment and torque balancing are both accomplished. If possible, the loft-increasing-moment is desired to be reversed and not balanced, since the negative face loft is more desirable to get the golf ball rolling sooner. The axial location of the main balance-weight body may need adjusting if the torque balancing with the additional internal weights changes the total weight; hence some iteration is needed between the axial weight position/magnitude and the location and amount of the inserted asymmetric balance weights. Once the whole balancing process is completed for the split-grip option, an adhesive is used between the shaft and upper grip parts to lock everything in place. After the adhesive is cured, then an external “skin” is applied over the upper metal grip. By USGA Rules the outside diameter of the upper grip with the cover needs to be less than 1.75 inch. In a split-grip application, by USGA Rules the total length of the putter needs to be greater than 38.5 inches, so that the distance between the actual grip and the weighted section can be a small as 1.5 inches. Additionally, by USGA Rules, the length of the weighted upper grip must be greater than 5.0 inches; and the external cross-section of the weighted section is circular in the split-grip option. For practicality, the putter length for the split-grip option is made just slightly larger than 38.5-inches, the gap between the main balance-weight body and the lower actual grip is made just slightly larger than 1.5 inches, and the main balance-weight body is slightly larger than 5.0 inches.
The above counterbalancing system can be designed to be a one-piece grip if desired to keep the total putter length less than 38.5-inches (for shorter golfers) or for aesthetic purposes. In this case the weighted section is abutted to the main grip with a cover over the whole main grip and either part or all of the main balance-weight body. The cross-section of the main balance-weight body and grip section in this option can have a flat region along the axial length of the grip and the main balance-weight body. The maximum diameter again is 1.75-inches, but the length of the main balance-weight body is not restricted. Again the internal offset weights are used to allow for balancing in all three degrees-of-freedom of motion and elimination of the undesired moments and torques. Finally, if a golfer insists on having more weight (moment in the Y-Z plane, as described later), then he can grip above the balance point. The balance point can be also be intentionally made further below the grip while still maintaining the torsional balancing and the eliminating or reversing the loft-increasing moment (X-Z plane moment, as described later).
For custom balancing an individual putter, weights of different lengths or density are judicially placed in internal holes in the main balance weigh body. Alternatively, for manufacturing a larger number of identical putters, the main balance-weight body could have holes of different dimensions so that no weights need to be inserted. In this way, the putters are balanced to pre-set standards as opposed to the individual golfer.